The Siren's Black Tide Rising

When a series of precision-engineered bank heists strike the East Coast, DS Mandy Smith thinks she's chasing a criminal mastermind.
She's wrong.
The thief leaves no fingerprints, no footprints - only a black shell marked with a number. Each shell leads Mandy deeper into a hidden world beneath the cliffs, where tunnels hum with stolen power and the sea itself seems to shift at his command.
The man calling himself The Tide caller isn't stealing money.
He's building something.
Something vast.
Something alive beneath the Humber.
As the coastline fractures, emergency channels fall silent and a towering structure rises from the deep, Mandy realises the truth: the Tide caller isn't planning an attack. He's preparing for a collapse he believes is already coming - and he's choosing who survives it.
To stop him, Mandy must descend into the heart of his creation, sabotage a machine that can rewrite the tide, and confront a man who sees himself not as a villain... but as the coast's last prophet.
The sea is rising.
The land is falling.
And the final chapter will drown them all.